2002 Pampera - rear calliper

[bob nr York]

Hello everyone -

I'm posting on behalf of a friend that I ride off-road with. His bike is a 2002 GG Pampera. Mechanically it goes on and on - but sadly the rear calliper seems unwilling to play ball. It's proven extremely difficult to bleed, for one thing. But - more basically - it's just too much brake for the bike, really. In that it's unnecessarily complicated - being a four piston brake - and thus at odds with the well-conceived simplicity of the rest of the bike.

I think I'm being optimistic here but are any other callipers compatible with the Pampera of this particular year, because my mate's really hoping he can replace it with another kind.

Thanks in advance everyone.